1. Field of the Invention
This invention is related to a contactless volume control device with adjustable gain and multi-output, and more particular to an output voltage modulation via a position sensing device.
2. Description of Related Art
Ordinary volume control devices have the advantages of simple structure and high reliability, whose output voltages are mostly controlled by a contact structure consisting of a conductive carbon film and an electric brush. But the output (location vs. output voltage relationship) applied to volume adjustment must be a logarithmic type so as to comply with the feelings of the human auditory, thus this kind of contact causes high manufacturing cost and the usage value thereof relatively low. The contact type has a certain service life, and if the contact interface is polluted, the voltage output will be affected and the service life will be shortened. Further, even a contactless type consisting of variable capacitors is also able to solve the above mentioned output problem, the manufacturing cost of this type is still high.
In fact, a common volume control device is a position sensing device. Currently the contactless position sensing technologies and patents mainly use the combination design of magnets and a Hall element to achieve the required voltage output. For example: a magnet with a special designed shape generates a special magnetic field to allow the Hall element to move therein, so that the output voltage has a linear relationship with the angle change of the magnetic field. Another example is to form a digital position sensor by using multiple sets of bipolar NS magnets according to the Hall element. Still another example is to use two groups of NS magnets respectively having n pairs of magnetic poles and n+1 pairs of magnetic poles, in association with two groups of Hall elements so that the variation of the output voltage is detectable by the two groups of Hall elements.
Most Hall elements are used as movable members due to the magnet's special shape to provide a special magnetic field, which allows a linear relationship existing between the output voltage and the position of the Hall element.
Further, assuming that the Hall element is designed as a movable member, the signal line movement problem must be dealt with Therefore, in contrast to the fixed Hall element, the movable magnet ensures the reliability of the Hall element wiring.
However, according to the prior art, it is necessary to consider the stability of the magnet magnetization and the distance between the Hall element and the magnet. The closer the magnet is to the Hall element, the Hall element becomes more influenced by the distance of the magnet and thus the resulting voltage output is also influenced, which is because the Hall element is sensitive to the variation of the intensity of the magnetic field. So that the distance (X) between the magnet and the Hall element and the output voltage (V) of the Hall element have the linear relationship with smaller scope. The solution is to increase the configuration number of the magnet and the Hall element, which, however, also increases the volume of the whole device. Further, mounting error and the consistency of each magnet are the issues that must be considered in increasing the configuration number of the magnet and the Hall element. Because either one of the issues will cause the Hall element to output unexpected voltages.
In addition, when installing multiple Hall elements and magnets, the installation error factors and the magnetic flux density of the magnet must be considered, which will cause the voltage output not ideal.